(1) Field of the Invention
The present invention lies in the area of methods and systems for guiding an aircraft—more specifically, a rotorcraft—during the approach to a landing point. More specifically, the present invention relates to such methods and systems that are organized so as to limit the noise discomfort generated by the rotorcraft within the environment near such a landing point, including, in particular, helicopter landing pads or heliports.
(2) Description of Related Art
The conditions governing the maneuvers of a rotorcraft approaching or departing from an identified and stored landing point are currently regulated. Within this context, it is customary to establish landing procedures to assist the pilot in guiding the rotorcraft, depending on the specific configuration of the environment near the landing point.
For example, one known approach to a given landing point consists of a procedure known as “VFR” (Visual Flight Rules). In a VFR procedure, the pilot of the rotorcraft relies on predefined approach instructions and external visual references, without receiving assistance from a piece of onboard equipment dedicated to the automated management of an approach trajectory to be followed. Such a VFR approach procedure requires that the pilot must have satisfactory visual contact with the landing point to be reached.
For example, another known approach to a given landing point consists of a procedure known as “IFR” (Instrument Flight Rules). In this case, the pilot has a piece of onboard equipment that allows the rotorcraft to be guided along a prescribed approach trajectory in order to reach the landing point.
The approach trajectory is defined by an approach route taken from an aeronautical database. In response to instructions from an air-traffic controller on the ground, the pilot selects, from the aeronautical database, an approach route that the rotorcraft should follow to the landing point. The approach route is commonly subdivided into several segments, in accordance with the identification of several waypoints. In particular, the following segments are defined:                an initial approach segment, defined between an initial approach fix (IAF) and an intermediate fix (IF);        an intermediate segment, defined between the intermediate fix (IF) and a final approach fix (FAF); and        a final approach segment (FAS), defined between the final approach fix (FAF) and a decision height or a decision point. The decision point is identified by coordinates stored in a predefined geodesic reference source, in accordance with a ground-height limit that the pilot of the rotorcraft takes into consideration in order to estimate whether he can or cannot complete the approach of the rotorcraft to the landing point. The decision point is commonly defined in accordance with a minimum descent altitude (MDA).        
The current position of the rotorcraft is also detected—specifically, by means of instrumentation present on board the rotorcraft, which instrumentation includes, for example, a satellite navigation system, such as a Global Navigation Satellite System (GNSS). The rotorcraft is then guided by the pilot to the landing point, with a minimization of the difference between the current position of the rotorcraft and the approach trajectory previously constructed by the computation means.
It should be kept in mind that the guidance of the rotorcraft may be managed by a human pilot assisted by means for displaying the information that is necessary for the implementation of these procedures, and/or may be managed, at least in part, up to the decision point, by means of specific functions that are implemented by an automatic pilot (autopilot).
In order for a rotorcraft to be guided in accordance with an approach trajectory, consideration must be given to the frequent presence of wind, whose characteristics are identified in terms of speed and direction by instrumentation that, in particular, is present on board the rotorcraft. It is commonly acknowledged that the characteristics of the wind may vary, depending on the geographic location of the landing point and in accordance with the climatic conditions.
The wind affects the forward progress of the rotorcraft. Consequently, the position of the rotorcraft must be adjusted continuously by the pilot, depending on the characteristics of the wind as measured on board the rotorcraft, in order to maintain the forward progress of the rotorcraft in accordance with the approach trajectory. More specifically, the pilot continuously corrects any discrepancies between the current position of the rotorcraft and the previously constructed approach trajectory, depending on the effects of the wind on the forward progress of the rotorcraft, with the characteristics of the wind being measured by onboard instrumentation.
Furthermore, the regulated conditions regarding the forward progress of a rotorcraft in the environment around a landing point also include, depending on the local regulations, a minimum tolerated threshold for noise discomfort generated by the rotorcraft. Beyond the regulatory constraints, it is desirable to minimize, as much as possible, the noise discomfort generated by the rotorcraft in the environment around a landing point.
The noise discomfort generated by rotorcraft are particularly noticeable during the landing phase, because of the operational mode of the rotor during the descent phase of the rotorcraft and because of the position of the rotorcraft as it approaches the ground. In order to limit the effects of the noise discomfort generated by the rotorcraft, consideration should be given not only to the noises produced by the rotorcraft, but also to the conditions whereby the generated noise is propagated toward the ground.
It is known that the noise discomfort produced by a rotorcraft during the approach phase to, or during the departure phase from, a landing point can be limited. For this purpose, it is known that an approach trajectory can be constructed in accordance with the approach route, taking into consideration the forward progress of the rotorcraft, such that the rotorcraft generates a limited amount of noise discomfort toward the ground. The goal of these provisions is to limit the noise discomfort to which residents are subjected, limiting the said nuisance to a level below a predefined threshold of tolerated noise discomfort.
For this purpose, it is known that a supplemental database can be used that contains rotorcraft flight domains that should be avoided, because those domains generate noise discomfort that have been deemed excessive with regard to a predefined threshold of noise discomfort. The said flight domains are identified according to the forward-progress modes of a rotorcraft that has a given structure and a given mass, and that is moving along a given ground slope. The information contained in the supplemental database can be used to construct a rotorcraft approach trajectory in accordance with the previously selected approach route.
In this regard, reference may be made to the document identified as EP 1730032 (EUROCOPTER FRANCE), which describes such a supplemental database containing flight domains that should be excluded when an approach trajectory is defined, because those domains have been identified as generating excessive noise discomfort.
Furthermore, it is also known that a rotorcraft approach trajectory can be defined that is based on the selection of one or more approach routes that were previously identified for a given landing point. The said selection is made on the basis of real-time on-the-ground measurements of the noise produced by the rotorcraft, such that the noise discomfort generated by the rotorcraft approaching the landing point can be limited.
In this regard, reference may be made to the documents identified as EP 0945841 (INST. ADV. TECH. HELICOPTER) and JP 2736045 (COMMUTER HERIKOPUTA SENSHIN GI), which describe such methods for the construction of a rotorcraft approach trajectory toward a landing point that limits the noise discomfort generated by the rotorcraft.
Thanks to the document identified as US 2012/296499 (KIRCHHOFER, ALAIN), it is also known that a route to be followed by a rotorcraft can be constructed and displayed, so as to avoid overflying sites that are sensitive to the noise discomfort generated by the rotorcraft. The said sensitive sites were previously identified in accordance with the noise commonly produced by the rotorcraft during flight, and are displayed in conjunction with the route to be followed, overlying a map of the overflown terrain.
Within this context, the goal of the present invention is to propose a method and a system for guiding a rotorcraft on approach to an identified landing point while limiting, as much as possible, the noise discomfort generated by the rotorcraft.